<!DOCTYPE html>
<html>
  <body style="margin:0px; padding:0px;">
    <div id="A" style="background-color: blue; height:5000px; width:5000px;">
      <div id="B" style="background-color: red; height: 3500px; width:3500px;">
      </div>
    </div>
  </body>
</html>
